Field of the Invention
The invention relates to a device for examining liquids that has at least one exchangeable sensor connected to an evaluation device through an interface module.
Such a device is used for example for the monitoring of liquids in sewage plants.
For inspecting liquids, until now calorimetric test devices have for example been used. They contain a test cell, a mixture of chemical reagents in solid or liquid form, weighed out precisely and of a composition optimally selected for the measuring task, and an evaluation and display unit. For carrying out the test, a small amount of the liquids to be examined is filled into the cell, mixed with the reagents, shaken up or, if appropriate, additionally heated. This produces a color reaction, the intensity of which is characteristic of the components to be demonstrated in the liquid. The color intensity is determined by the evaluation and display unit and converted into a concentration of the substance sought. A disadvantage of this type of liquid examination is the relatively complicated procedure for the measurement, which requires knowledge of laboratory techniques on the part of the user, and also the high price of the evaluation and display unit.
Furthermore, paper-based or plastic-based test strips are known. These have applied to one end of them chemical reagents that are adjusted to the paper and specific for the substance to be detected. The test strips are dipped into the liquid to be examined. If the substance sought is contained in the liquid in a concentration that is not negligible, it produces with the reagents on the paper a color reaction, the intensity of which is a measure of the concentration in the liquid of the substance sought. No sample has to be taken, the test strip can be dipped directly into the liquid to be examined. A known example of this type of liquid examination is that of pH test sticks. A disadvantage of the test sticks is that only simple ion-selective reactions can be realized. Biological parameters such as the biological oxygen demand or more complex chemical parameters such as the chemical oxygen demand of a liquid cannot be determined with them.
Furthermore, small compact analysis systems with a volume of approximately 50 cm3 are known. The liquid to be examined is introduced by a pipette. The analysis system is then disposed in a separate external evaluation and display unit. This unit contains devices in the form of mechanical and/or electroosomotic pumps, with the aid of which the liquid samples can be moved through channels in the analysis system. The unit also provides the auxiliary energy for the detection of the component sought. In the evaluation, electrochemical and/or optical detection methods are carried out. Considerable auxiliary energy is required for this purpose. The disadvantage of this type of liquid examination is that an expensive and complicated external evaluation and display unit is required.